Cascaded pretreater for removal of nitrogen



May 17, 1960 V. O. BCWLES CASCADED PRETREATER FOR REMOVAL OF' NITROGENFiled Oct. 28, 1957v ENT cAscAnlin PRET'REATER rol;` REMOVAL or NITRoGENVernon 0. Bowles, Rye, N. V.`, assigner to Socony Mobil Oil Company,Inc.,va corporation 'of New! York ,y

The presentinvention'relates to the pretreatment'i'of u of the organicsulfur compounds present straight vrunk gasoline the concentrationv oforganic nitrogen -cornpounds is reduced to a level -at which theon-stream time of platinum-type catalystsis not substantially` reduced.However, underV the same conditions at which 90,1:lercent or more oftheorganic sulfur in thermally c'racked'gasoline is removed, the nitrogenlevel of the treated thermal gasoline is sufficiently high to markedlyaffect the o nstream time of reforming'unitsemploying nitrogen-sen'-sitive reforming .catalysts such las platinum-type catalysts..v Theincreased severityrequired dto produce satisfactorily denitrogenizedstock is illustrated by the following hydrocarbon mixtures containingnitrogen compounds v,

prior to subjecting said hydrocarbon mixtures to conversionV over anitrogen-sensitive catalyst in the presence of hydrogen and,moreparticularly, to the pretreatment of hydrocarbonmixture's containingnitrogen compounds bel fo're' subjecting 'said hydrocarbon 4mixtures toconversion over a platinum-type catalyst in the presence of hydrogen. 1p

With the increasing use of platinum-type catalysts and other'catalystswhich are 'sensitive to nitrogen and the expanding application ofhydrocarbon conversions to stockswhich have heretofore notbeen deemedhydrocarbon mixtures requiring catalytic treatment, deactivation ofcatalysts suitable for such hydrocarbon conversions as reforming,hydrocracking, and hydrogenating by organic nitrogen compounds hasbecome a problem which in the` past had not been of suilcient importanceto require considerationor the presence of organic nitrogen compounds inthe'feedito a hydrocarbon conversion was not recognized as a probablesource of operational diiculties. Thus, when designing' reforming unitsconsideration was given primarily to` the*A removal of sulfur from thefeed. Sincemost charge stocks 'were low in the concentration of organicnitrogen compounds no considerable`v operational fdiiculties ysuch' :pasrapid deactivation ofthe catalyst were encountered. v`Novv, however,gasoline components which without reforming previously satisfied thelower gasoline anti-knock requirements of a few years ago mustcatalytically be reformed to meet thehigher' anti-knock requirements ofpresent day cars.

COlllpIISOIlSI To Produce 1- To Produce satisfactorily satisfactorilyDesulturized Denitrogenized Reformer Reform er Charge Stock ChargerStock Pressure, Vp.s.i.g 425'- 425 Temperature, F. 675 675 v S.c.f.Hydrogen/Bbl. Charge.; 500 2,000 Space Velocity, v./hr./v. ...'.U r 5 2v ATo those skilled theartit is that a :decon-i ratio, lowerspacevelocity) requiredforadequa'te nitro- Whereas, heretofore Acrackingstocks I--have not 'been hy' drogenated, consideration is now' beinggiven to -hydrogenating. orhydrogenating and cracking of vsuclistocks toprovide improvedcharge stocks .for conventional cata'-A lytic crackingor to provide improved charge stocks for catalytic reforming andimproved diesel'fuels andimproved-domestic heating fuels. A particularlygood example Aillustrative of the situation and illustrative'of .themeans provided by the present invention Vfor'solving the problem isthatA of ythe, reforming of thermallyv cracked gasoline components;

u ntil the antieknockrequirementsfor motor vehicle gasoline rose topresent day levels 'of'about lOOoctane (RON-P3 cc.Tl-`;L) and higher,the octane rating -fof leaded blends containing thermally cracked-gasoline..was statisfactory. Consequently, most'v catalytic Areformingunits designed. and built prior to 41.957 were designed to processAstraight runI gasoline. The concentration lof organic nitrogen compoundsin most straight run gasol-ines visyery v.low compared .to theconcentration of organic nitrogen compounds in thermally crackedgasolines."v I Furthermore, it -would appear that'the organic nitrogenvi compounds in straight run gasoline are morereadily de-` composed thanthe organic nitrogen compounds present in thermally cracked gasoline.Consequently, when straight run gasoline is subjected vto processingunder conditions required to remove upwards of 90 percent' f priorconcept of acceptable anti-knockrating were notV gen conversionto-,vola'tile hydrogenlderivatives thereof.` A,I-Ieretof'ore thevprimary concern of those designing and -building units for'. thereforming ofnaphtha to produce gasoline of improved anti-knockproperties has been the removal of sulfur. Accordingly, many reformingunits, especially those wherein a platinum-type catalyst is employed,have been designed with -decontaminating units .employing processseverity sulficient only .for 'decontamination ofstraight run stock.With the increased demand for `motor gasolines of' greater and greater-antiknock'rv rating yit has/become necessaryto reform charge stocks'whichV heretofore have not been considered as reformercharge stocksbecause the anti-knock'ratings of the blends containing, thefractionwere satisfactory Without reforming. Typical' of these stocks, whichunder the deemed stocks'requiring reforming'is thermally cracked aphtha.e

o' Thermally cracked naphthas have nitrogen contents ranging from about30 to aboutfO() parts per million (p.p.rm.). Thermal'ly cracked naphthasalso contain about 10`to about 40 percent by volume ofy olenic hyuConsequently, when 'a "naphtha such 'as thermally cracked naphtha,hereinafter-designated thermal naphtha or thermal gasoline,having ahighconcen` tration Vof nitrogen', i.'e.,in` excess of V5 pipm'., is to bereformed additional: hydrogen -is necessary to 'deconi taminate thestock having, the high nitrogen Iconcentration. Furthermore, it has beendiscovered recently that the conditions necessaryy -forthe reduction ofthe nitrogen concentrationv ofja .reformer charge stock to an innocuouslevel are more severe than those required to re movel k percentormoreflof the sulfur from a reformer charge stock. On the other hand,it is not usualgfor the volume ofnaphtha vto -be reformedrhaving arelatively high nitrogen content to represent only about 20 percent Yor'lessi'of the total volumeof naphtha to be reformed.

Consequently, itis not economical to subject the entire supplyof'reformer charge naphtha. to the severe condi-V less of-thesupply.

ICC PafeatedMay11fz,19so

gas oil, or catalytic gas oil the organic nitrogen cornpounds areconcentrated in a relatively minor portion of the charge.

Accordingly, the present invention provides a method of reducing in aseparate decontaminating operation the nitrogen concentration of ahydrocarbon fraction having a relatively high nitrogen concentration ofabout 30 to about 30D-ppm. to a nitrogen concentration which does notsubstantially reduce the on-Stream time of a hydrocarbon conversionemploying a nitrogen-sensitive catalyst, mixing the at least partiallydecontaminated hydrocarbon fraction with a hydrocarbon fraction having arelatively low nitrogen concentration of about to about 3 ppm.,hydrodecontaminating the mixture to reduce the concentrations of sulfurand nitrogen to acceptable levels at which the on-stream time of thecatalyst is of industrially practical length and the sulfur content ofthe mixture is not greater than about 5 to about 20 p.p.m., andsubjecting the hydrodecontaminated mixture to ultimate conversion atconversion temperature, pressure, hydrogen to feed ratio, and spacevelocity over a nitrogensensitive catalyst.

f Thus, for example, the hydrodecontaminated charge stock for a reformeremploying a particle-form, solid, platinum-type, reforming catalyst mustcontain not more than about l p.p.m.rof nitrogen to maintain anindustrially practical on-Stream period. i The method of the'presentinvention provides for the application of suitable conditions oftemperature, pressure, space velocity and ratio of hydrogen tohydrocarbon mixture to the minor portion of the charge to the ultimateconversion having the relatively high nitrogen concentration in aseparate operation with .a minimum of equipment `in addition to thatrequired to decontaminate the major portion of the charge to theultimate conversion which requires minimum or no additional gascompression, and has high thermal eciency. Since the present inventionis basically an invention `involving a sequence of operations thedescription of the invention as applied to hydrodenitrogenizing reformercharge stock is applicable to the hydrodenitrogenizing of otherVhydrocarbon mixtures hydrodenitrogenized for other ultimate conversionsover nitrogen-sensitive catalysts such as hydrocracking topped crudes',gas oils and the like, and hydrogenating or hydrolinishing hydrocarbonmixtures such as kerosines, diesel fuels, jet fuels and the like.Illustrative of the method of the present invention is the treatmentofireformer charge stock comprising a portion having" a relatively` highconcentration of organic nitrogen compounds and a portion having arelatively low concentration of organic nitrogen compounds. For example,the charge to a reformer employing a platinum- 'i type, particle-form,solid, Vreforming catalyst comprises about 20 percent by volume ofthermal naphtha containing about 30 to about 300 ppm. of nitrogen andabout 80 percent straight run naphtha containing about 0 to about 5 ppm.of nitrogen.

The thermal naphtha is pumped at a pressure about 175 p.s.i. higher thanthe pressure inthe hydrodenitrogenizing or vsecondary reactor, to ensurea pressure dif-l ferential sufcient to drive the thermal naphtha througha heater, the secondary and primary reactors, heat exchangers and otherequipment to the' suction side of the pump charging the reformerreactors. Preferably, to overcome or reduce the tendency of the thermalnaphtha tov foulv heater exchanger tubesat least a small quantity, eig.,about 50 to about 100 cubic feet of reformer recycle gas per barrel isinjected into the stream of thermal naphtha downstream of the thermalnaphtha charge pump and vupstream of the ythermal naphtha heatexchangers and heater. The preheated naphtha and the aforementionedVrecycle gas liow to a heater wherein the. thermal 4 naphtha is heatedto a temperature suitable for the hydrodenitrogenation thereof. Fromlthe thermal naphtha heater the thermal naphtha ows to the secondarydecontaminating reactor. Between the outlet of the thermal naphthaheater and the inlet of the secondary decontaminating reactor, theportion of the hydrogen-rich reformer recycle gas (containing at leastabout 70 percent by volume of hydrogen) flowing directly from thereformer gas-liquid separator or from the primarydecontaminating circuitor from both, that is required to make up the desired ratio of hydrogento thermal naphtha charge, is mixed with the thermal naphtha.Alternately, all of the hydrogen-rich gas can be injectedinto thethermal naphtha stream downstream of the charge pump 25 and upstream ofthe heat exchangers to more effectively control fouling. The heateroutlet temperature is controlled and regulated to maintain an averagetemperature in the sngary decontaminating reactor of about 650 to aboutThe straight run naphtha ows vthrough an absorber where it is inintimate contact with the gases and vapors from the various gas-liquidseparators forming a part of the hydrodecontaminating unit. From theabsorber the portion of the reformer charge stock having a low nitrogencontent, i.e., in this illustration the straight run naphtha, flows to aheat exchanger where the straight run naphtha is in indirect heatexchange relation with the total eiuent from the primary decontaminatingreactor. The thus preheated straight run naphtha ows to the straight runnaphtha heater wherein the temperature of the straight run naphtha israised to that required for the reaction in the primary decontaminatingreactor. Downstream of the straight run naphtha heater and upstream ofthe primary decontaminating reactor, the eiuent of the secondarydecontaminating reactor is mixed with the heated straight run naphtha.The mixture of the eiuent of the secondary decontaminating reactor andthe heated straight run naphtha flows to the primary decontaminatmgreactor. Prior to entry of the aforesaid mixture into the primaryydecontaminating reactor hydrogen-rich reformer recycle gas, preferably,or any other hydrogenrich gas is mixed with the mixture of the at leastpartially denitrogenized .thermal naphtha and untreated straight runnaphtha. Usually, about 500 to about 2000 cubic f eet ofvrecycle gas(containing about 70-90 percent by volume of hydrogen) per barrel oftotal charge stock is mixed with mixture of the at leastpartiallydenitrogenized thermal naphtha and the untreated straight run naphtha.The effluent from the primary-decontaminating reactor compriseshydrogen, hydrogen derivatives of contaminantsoriginally-present in thenaphthas, and C1+ hydrocarbon's. The eiu'ent from the primarydecontaminating reactor'flows through heat exchangers and a cooler toreduce the temperature of the primary reactor effluentv to that atwhichrCg-lhydrocarbons at least partly separate from .hydrogen and thevolatile hydrogen derivatives of contaminants. t

`In the gas-liquid separator hydrogen, C1 to C3 hydrocarbons, hydrogensulde, ammonia, and other gaseous constituents of the primary efliuentat least partly separate from C4 and heavier hydrocarbons. Theuncondensed portion of the primary eftluent is vented to the renery fuelsystem through fan absorber for 04+ hydroshown through pipe 1, by pump Zand discharged into .pipe 3. At some point ,4, between pump Z andthermal gen-containing gas, e.g.*, reformer recycle gas, flows A throughpipe-"3 to heat exchanger 6 wherethemixture is 1n lndirect heat exchangerelation with at Ileast `a'portion ofi the total eflluent owing fromprimary' decontaminating reactor 33. From heat Vexchanger 6 the thermalVnaphtha .and hydrogen flow through pipe 7 toV coils 8 in heater 9. Inheater 9 the thermal naphtha and hydrogen is heated to, a temperatrn'esuitable for bringing about the hydrogenation ofv the organic compoundspresent in thefthermal naphtha vatfthe pressure and the hydrogen partialpressurefexistingin secondary decontaminating' re# actor 12.-. Forexample, fatf425 to 850 p.s.i.g.'v andv with reformer gas separator,eg., at 600 p.s.i.g. or more, it is necessary to compress the reformerrecycle gas to a higher pressure. vHowever, generally'- it is notdesirable to operate the stripperatsuch higher pressures. yAccordingly,reformer recycle gas at the'pressure of the reformer gas separator tlowsas previously describedv to the stripper 22 and thence through conduitsY55 and 21 to absorber 18 while the hydrogen for use in the secondarydecontaminating reactor flows from the 4reformer recycle gas separator(not shown) through conduit 75 to conduit 78 to conduit 70 and thesuction side of compressor71;5" Compressor 7=1 compresses the reformerrecycle gas -to afpressure higher than that of the secondarydecontaminatingreactor 12 and ydischarges the recompressed gas intoconduit 72. With valve 80 controlling the amount of gas flowing throughconduit 74 toconduit 5 (the 50 to 100 cubic feet-'required in pipe 3 ashereinbefore de- 500 to 2000. cubic feet ofw hydrogen per vbarrel ofthermal naphtha a temperature of about'675 to 775 F. in; secondarydecontaminating reactor 12l provides satisfactory results. `v

The heated thermal naphtha ows lfrom coils 8 through pipek 10 to conduit11 where the thermal naphtha is mixed with the balance of the hydrogennecessary tof providey about 500 to about 2000 cubic feet of hydrogenper barrel of thermal naphtha. required-for bringing about the reactioncan be admitted scribed) the ybalancent` the f recompressedreformer re'-cycle gas (enough'to make about 500-2000'c.|f./b'. of

'thermal naphtha in' secondaryl decontaminating reactor 12) Y:flowsthrough conduits 73' and-7S to conduit 11 i* where the compressedreformer recycle gas is mixed'with Alternately, all of the hydrogenthrough conduit 5 and pipe 3. When the secondary decontaminatingfreactoris being operated latv a pressure of abouti450 -to about 550 p.s.i.g.thefaforesaid additionalhydrogen is "obtained from the stripper overheador Vdirectly from the gas separator of the reforming unit operating at apressure in suicierit excess of about 450 to about' 550 p.s.i.g. toovercomethe back pressure ofthe intervening piping or from'both. Whenthe secondary dccontamin'ating reactoris being operated at afpressure psubstantially higher than that ofv the gas separatorof the reformingu'nit,i.e., at-@pressures greater than about 55.0

up toab'out SOO'psJiggthe hydrogen for hydrogenating thethermal naphthain thev secondary decontaminating the heated :thermal naphtha -asdescribed hereinbefore. `Wlien'desirable all of the hydrogen required inthe secondary` decontaminating reactor 12 can flow from conduit 75through conduits 78 and 70 to compressor 71, thence through conduits 72and 74 under control of valve 80, to conduits 5 and 3l. o

The mixture of 'heated thermal naphthaand about 500 to about 2000 cubicfeet of hydrogen per barreloftheb. mal naphtha flows preferablydownwardly through secl ondarydecontaminatin-g reactor 12 in intimatecontact with a sulfur-and nitrogen-insensitive hydrogenation catalystsuch as a mixture of oxides of cobalt and molybdenum supported onalumina. Y Y f In secondary decontaminating reactor 12the` nitrogen v Qconcentration of the C44' portion of 'the thremal naphtha reactor isobtained from the gas separator of the reform#` p ing'unitandcompressedto a pressurein 'sullicient excessv of that ofthe secondarydecontaminatingrreactor to overl.

comezthe back 'pressure of theintervening piping and equipment. I .l 1Thus, 'when the secondary decontaminating reactor. is being operated ata pressure of'about 425' p.s.i.g., hydrogen-containing gas, e.g.,atleasta portionof'reformer recycle gas, ilows rfrom the reformer gasseparator (not shown) through conduit 75 (with. valve' .76' closed)through pipei77 to stripper 22 wherein the recycle gas brings aboutthestripping of the volatile hydrogenderivatives of thiefcontaminants'fromthe primary condensate.

gas separator-(not shown) and fromv the strippen, When` the additionalhydrogen is-obtained;l directly from thereformer recycle4 gas separator(not shown) but also., from the stripper atleast a portionv of thereformerrecycle gas flows romA conduit 7 5 through. conduit 77 in theamount necessaryY to strip the primary condensate of Iall but tolerable'itraces of volatile' hydrogen derivativestofj contaminants in the.original feed. `From shipper 22 thehydrogen as apart of theoverheadlfrom stripper 22 flows 'through conduit 55' to conduit 11. Thebalance oft thev required hydrogen flows from conduit 75 through conduit78 to conduit ,11 under control` of 'valve 79.

Whensccondary dccontaminating reactor 12 is being operated at aVpressure-in excess of the pressure'in the isreduced to a'concentrationsuch that lwhen mixed with the straight run naphtha and processedfurtheras hereinafter described' the nitrogen concentrationV of the Cd'Vportion-of the mixtureis not more thanA about l p.p.m.

'when tliermixture is to be reformed 'overanitrogen-sensitiveplatinuniz-ftype reforming catalyst. ."Thu's, the feedfor Ythe reforming unit in this illustration isrrabout 2O percentthermal naphtha and about percent straight runnaphtha and the nitrogenconcentration of the thermal'naphtha after being processed in thesecondary decontaminating reactor is reduced to about 2-20 p.p.m. Thisat least partially denitrogenized thermal naphtha togeth'erwith theproducts of the reactions which take place in secondary decontaminatingreactor 12 form the secondary decontaminating reactor effluent. Thesec'- ondary `decontarninating reactor ellluent ows from secondarydecontaminating reactor 12 through conduit 32'.

In conduit "32 the secondary decontaminating reactor ef# lluentis mixedAwith heatedk straight run naphtha and the additional hydrogen requiredto provide about 500 to about 1000 cubic feet of hydrogen per barrel ofnaphtha treated in primary decontaminating reactor 33.

@In the primary decontaminating reactor the mixture of partiallyhydrodecontaminated thermal naphtha and the unprocessed straight runnaphtha, the mixture containing not more than about 20 p.p.m. ofnitrogen,4 is contacted with ya sulfurand nitrogen-insensitive catalyst(which can be the-same asY or different from the catalyst in secondarydecontaminating reactor 12 such as a mixture of oxides o f cobalt'andmolybdenum supported on alumina) -in the presence1ofabout 500 to about1000 cubic feet of hydroy genio Vreduce the nitrogen concentrationof theC4+ portion' of the aforesaid mixtureof partiallydecontaminated anduntreated i about 1 p.p.m.

The straight run naphtha isheated to the reaction temperaturerequired'in-primary. decontaminating reactor 33 as describedhereinafter'. Y

straight run naphtha to not more than Straight run gasoline is drawnfrom a source not shown through pipe 13 by pump 14 and discharged intopipe 15. The straight rurr naphtha ows through pipe 15 to a kpluralityof branches, e.g., two, i.e., pipes 16 and 17 and thence lto absorber 18in which'valuable hydrocarbons are absorbed from the gases and heatexchanger fouling precursors such as oxygen are stripped-from thenaphtha feed. Stripper overhead from stripper 22 gas .flowing throughconduits 55 and 21 and uncondensed primary decontaminating eilluentflowing from gas-liquid separator through conduit 19 are intimatelycontacted with the straight run naphtha in absorber 18. The straight runnaphtha absorbs primarily C4 and heavier hydrocarbons `fromthe gaseswhile the gas strips oxygen and other heat exchanger fouling materialsand Water from the naphtha. The absorber residue `gases ilow fromabsorber 18 through conduit 23 ,to plant fuel or other uses while `thestraight run naphtha leaves absorber 18 through pipe 24. v

The straight run naphtha ows through pipe 24 to the suction side of pump25. Pump 25 discharges the enriched straight run naphtha into pipe 26 ata pressure higher than the pressure in primary decontaminatingreactor33. The naphtha flows through pipe 26 to heat vexchanger '27 Where theenriched straight run naphtha is in indirect heat exchange relation witha major portion or all of the eiuent from the primary decontaminatingreactor 33 as hereinafter described. From heat exchanger 27S theenriched straight run naphtha flows through pipe 28 to coil v29 inheater 30. Y -In heater 30 the preheated, straight run Vnaphtha isheated to a temperature suitable for bringing about desulfurization,eg., about 700 to about 825 F. From heater 30 the hot, straight runnaphtha ows through pipe 31 to conduit 32. As stated hereinbefore, inconduit 32 the hot, straight-run naphtha is mixed with the secondarydecontaminating reactor effluent and the amount of hydrogen required toprovide with the hydrogen in the secondary decontaminating reactoreffluent, about 500 to aboutlOOO cubic feet o f hydrogen per barrel ofmixed naphtha owing into primary decontaminating reactor 33. Thishydrogen preferably `is drawn frorngconduity through conduit 34 or fromconduit 68 .through conduit 34 .or from both conduit 55 Vand conduit 68through conduit 34., Y'

The mixture of secondary decontaminating reactor effluent, heatedstraight run naphtha and suchv additional hydrogen as required ilowsthrough conduit 32 into primary decontaminating reactor 33. In primarydecontelaminating reactor 33 the aforesaid mixture is intimatelycontacted with a sulfur-insensitive catalyst, eg., a mixture of cobaltand molybdenum oxides on alu-mina ata temperature within the range ofabout 650 F.to about 750i F. In primary decontaminating reactor 33 thesulf ur concentration of the mixed naphthas is reduced by conversion tohydrogen sulfide which is rejected in stripper 22 or dehexanizer 51 to alevel at which the reforming catalyst is net deactivated to anyappreciable extent and the corrosion of the metal parts of the reformingunit is at a practical minimum. In a similar manner nitrogen compoundsand other contaminants are hydrogenated to yield volatile hydrogenderivatives vof said contaminants which are rejected in stripper 22 ordehexanizer. 51.

l As illustrated there are at least two paths through which the totaleflluent, `i.e., non-condensible and condensible components, of thevprimary decontaminating reactor can vflow to transfer at least a majorportion of the heat in the total efliuent from the primarydecontaminating re-zv actor to the charge-naphthas. Preferably, a minorportion of the total eflluent of the primary decontaminating reactor(hereinafter designated primary reactor) is brought into heat exchangerelation with the minor portion of the charge naphtha, i.e., the crackednaphtha while the maior portion of the total eiuent ofthe primaryreactor is brought into heat exchange relation with the balance .of thecharge naphtha.l Alternatively, the entire totalweflluent of the primaryreactor is brought into heat exchange relation with the minor portion ofthecharge n aphtha and then brought into .heat exchange relation withthe balance of the charge naphtha. s. Preferably a minor portion aboutequivalent to `the volume of cracked naphtha flowing through pipe 3flows through conduit 36 under control of valve 37 to heat exchanger 6where the minor portion of the total effluent from primary reactor 33 isin indirect heat exchange relation with the cracked naphtha. .Thebalance of the total effluent from the primary reactor, ows throughconduit 38 under control of valve39 to heat exchanger 27 where the majorportion of the totaleluent is in indirect heat exchange relation withthe straight run naphtha flowing through pipe 26. With valves 39 and 81open and valve 40 closed the aforesaid minor portion of the total eluentfrom primary reactor v33 ows through conduit 41 to conduit 42. The majorportion of the total-effluent from primary reactor 33 flows from heatexchanger 27 through conduit 43 to conduit 42 where the major portionand the minor portion of the total effluent from the primary reactor 33mix and flow to heat exchanger 45. f v

Alternatively, with valve 39 closed and valve 37 open the entire totaleilluent of primary reactor 33 flows through conduit 36 to heatexchanger 6 where the entire total efuent is in indirect heat. exchangerelation with the cracked naphtha. With valve 81 closed and valve 40open the entire total eluent ows from heat exchanger 6 through conduit44 to conduit 38 and-thence to lieat'texchanger 27 where the entiretotal eifluent. from primary reactor 33 is in indirect heat exchangewith the straight run naphtha. From heat exchanger 27rtheentire totaleffluent from primary reactor 33 ows through conduits 43. and 42 to heatexchanger 45.

In heat exchanger 45 the entire total eiuent of primary reactor 33 is inindirect heat exchange relation, with the condensate separated inseparator 20 from the total euent from primary reactor 33 as describedhereinafter. In heat exchanger 45 the primary reactor eluent gives upits heat to the condensate thereby heatingthe condensate to atemperature at which volatile hydrogen derivaties of contaminants andsome hydrocarbons are stripped from the liquid phase at the pressureexisting .instripper 22. Alternately, the, condensate is heated to afeed temperature suitable for bringing about the separation of hydrogenand hydrogen derivatives of contaminants from the major portion of thecondensate at the pressure existing .in dehexanizer 51. v

From heat exchanger 45 the primary reactor eluent -tlows through conduit46.to cooler V47 where itis cooled to altemperature such that Vat thepressure existing hydrogen, a significant proportion of C1. to C4hydrocarbons and hydrogen derivatives of contaminants are not condensedand a major portion of the C4| hydrocarbons are condensed. From cooler47 the cooled primary reactor efiuent flows through conduit 48 togas-liquid separator 20.

In gas-liquid separator 20 the condensed hydrocarbons are separated fromthe uncondensed hydrocarbons, hydrogen, and hydrogen derivatives ofcontaminants. Y The uncondensed hydrocarbons, hydrogen, hydrogensulfide, etc., ow from gas-liquid separator 20 through conduit 19 toabsorber 18 as described hereinbefore. The condensed hydrocarbons aswell as some dissolved light hydrocarbons and hydrogen derivatives ofcontaminants ow through pipe 49 to the suction side of pump 50.. Frompump 50 the primary reactor eluent condensate, hereinafter `designatedprimary condensate, ows either to a stripper 22 or to a dehexanizer 51.It is very unusual for a stripper and a dehexanizer to be included inthe same pretreating unit. However, forparticular local reasons one isoften preferred to the other. The how of primary condensate through astripper will be described rst and t 9 then Vthe*alternativ`e` lflowthrough a dehexanizer will'be described.r 1 f The flow ofprimary'condensate-is'from heat exchanger 45 through pipe 52 (valve 53opent valve 54 closed) to stripper 22. In stripper 22 somelight'hydrocarbons together with residual hydrogen, hydrogen sulfide,and other hydrogen derivatives of contaminants, etc., are taken asoverhead through pipe 55 and thencetoiabsorber 18, or to reactor 12, `orto reactor 33. To facilitate stripping light hydrocarbons,` hydrogensulfide and other hydrogen derivatives of' contaminants from the primarycondensate, recycle gas from the gas separator in the reforming unitflowing therefrom through conduit 75 is introduced into stripper 22through pipe 77. The C4+ and heavy hydrocarbons and some dissolved lighthydrocarbons form a bottoms fraction in stripper 22. The bottomsfraction contains only the very small amounts of contaminants tolerablein the reformer charge. The bottoms flow from stripper 22 through pipe56 to the reformer unit.

When a dehexanzer is used in placeof a stripper the primary condensateflows (with valve 53 closed and valve 54 open) through pipe 52 to pipe57 and thence to dehexanizer 51. In dehexanizer 51 an overhead of C6 andlighter hydrocarbons together with hydrogen, hydrogen sulfide, etc. istaken through pipe 58 to accumulator 59.

From accumulator 59 the hydrogen, hydrogen sulfide, etc., andlighthydrocarbons flow through pipe 60 to the refinery fuel system. The C orC@ and lighter hydrocarbons separated as liquid in accumulator 59 flowthrough pipe 61 to stabilization and use or to be otherwise processed.

drocarbons. Any means for maintaining the vaporizing temperature indehexanizer 51 other than the reboiler described can be used. Thebalance orA the net bottoms of dehexanizer 51 flows through pipe 68 tothe reformer, feed pump or reformer feed rstorage.

It will he manifest to those skilled in the var-t that the foregoingdescription of the treatmentof thermal gasoline and straight rungasoline is illustrative of the treatment of i 50 treatment a minorportion having a relatively high nitroa the ultimate feed to ahydocarbon conversion vin which gen content is processed in' a separateor secondary decontarninating reactorA under conditions severe enough toreduce the nitrogen content of said minor portion to a level such thatwhen mixed with the major portion of the ultimate feed to saidhydrocarbon conversion aud the total ultimate feed subjected tohydrodesulfurization conditions usually milder than conditions in thesecondaryV decontaminating reactor the so pretreated ultimate feed has anitrogen content which does `not appre'ciably decrease the on-stream.time of a nitrogen-sensitive catalyst employed -in said hydrocarbonconversion. t

I claim: v

1. The method for the conversion of a hydrocarbon fraction containing atleast 30 p.p.m. of nitrogen in the form of organic nitrogen compoundswhich comprises,

treating said fraction with hydrogen .in the presence of a nitrogenandsulfur-insensitive solid catalyst in a first reaction zone underhydrodenitrogenizing conditions subf stantially more severe thanrequired merely of hydrodesulfurization to obtain a firstl effluent ofsubstantially reduced organic nitrogen compound content, mixing saideiliu'ent with asecond hydrocarbon fraction having a relatively low:concentration of organic lnitrogen compounds andcontainingalsoimpurities in the form of" organic sulfur compounds, saidsecond ifraction' comprisng the maior portion of saidmixture, treatingsaid mixture with hydrogen in the presence of a nitrogenandsulfur-insensitive solid catalyst in a secondv reaction zone underhydrodesulfurization conditions to obtain a second eiiiuent streamcomprising C1+ hydrocarbons and hydrogen derivations of nitrogen andsulfur produced invsaid treatments, separating `said eiuent into apluarlity of fractions, one kof said fractions being the C54-hydrocarbon fraction of s-ubstantially reduced nitrogen .content andsubjecting said 4(Q -,-lhydrocarbon. fractiontoa conversion in contactwith a nitrogen-sensitive solid catalyst: 2. The'method as set fortlrinclaim l in which the remainder of said separated fractions is 4recycledto the first and second reaction zones. 3. The method as set forth inclaim -1 in which at least a portion of the hydrogen introduced -intothe firs-t `re`l l action zone is reformer recyclegas.

4. The method as set forth in claim lin which the' first fraction is athermal naphtha.v

45.`The method as set forth in claim l' `inwhich the first fraction is a-thermal naphtha and the .said separated Cgi-'hydrocarbon fractioncontains not more than about l p.p.m. of nitrogen.

6. 'Ihe method as set forth in claim 1 in which the said first fractionis a lthermal naphtha, the said second fraction is a straight runnaphtha, and the said separated C54- hydrocanbon fraction contains notmore .than about 1 p.p.m. of nitrogen. n

7. In the method for reforming in contact with a nitrogen-sensitivesolid catalyst aA straight run naphtha in admix-ture with a thermalnaphtha which initially contains a relatively `high concentration oforganic nitrogen compounds equivalent to atleast about 30 p.p.m.nitrogen,

the improvement which comprises contacting in an auxiliary reaction zonesaid nitrogen containing thermal naphtha with hydrogen inthe presence ofa nitrogeninsensitive catalyst under-severe hydrodenitrogenizingconditions whereby the content of organic nitrogen compounds within theboiling range of said thermal naphtha is substantially reduced, mixingthe eiuent from saidl auxiliary reaction zone with a major proportion ofsaidY straight run naphtha, contacting in a primary'reaction zone saidmixture with hydrogen inthe presence ofa nitrogen-insensitive solidcatalyst under conditions less severe Vthan in said auxiliary reactionzone to obtain a primary reaction zone eluent comprising Cl-ihydrocarbons, hydrogen, and hydrogen compounds of nitrogen and sulfur derivedfrom the organic nitrogen and sulfur compounds present in said .thermalnaphtha and straight run naphtha, separating said efiiuentinto pluralityof fraction including a C5 hydrocarbon yfraction of substantiallyreduced nitrogen content and reforming said C5+ hydrocarbon fraction incontact with anitrogensensitive solid catalyst. I

8. The improvement as set forth in claim 7 wherein a minor portion ofthe primary reaction zone efiiuent passes in heat exchange relation withthe thermal naphtha feed to the auxiliary reaction zone and the majorportion of said primary reaction zone effluent passes in heat ex-fsevere than required for hydrodesulfurization to obtain a first efiiuenthaving a substantially reduced content of organic nitrogen compounds,mixing said first eluent with a straightrun naphtha in proportions suchthat said straightrun naphtha is the maior component of the resultingmixture, said straight run naphtha. containing impurities in the form oforganic sulfur compounds with only arelatively low content of organicnitrogen impuri ties, treating said mixture with hydrogen in thepresence of a nitrogenand sulfur-insensitive solid hydrogenationcatalyst under hydrodesulfuriz'ation conditions to obtain a secondeffluent stream comprising C1+ hydrocarbons, hydrogen, and hydrogencompounds oit-nitrogen and sul- Afur derived `from organic nitrogen andorganic sulfur impurities originally contained in the said naphthas, andseparating from said euent a reformer feed `fraction comprising C54-hydrocarbons said fraction having a nitrogen content not inexcess ofabout 1 p.p.m.

5 type, reformingv catalyst.

12 10.- The method' as set forth in claim. .7"whereinthenitrogen-insensitive catalyst is a mixture of cobalt and molybdenumoxides;v supported on alumina and the nitrogen-sensitive solid'gcatalystis a particle form, -platinumf `ReferencesVCited'in the file orfitliispatent i UNITED STATES PATENTS 2,760,907 Ariane et a1. Aug; 2S, 19562,793,170 sales et a1. May 21, 1951.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No2,?937Q134 May 17 1960 Vernon 0o Bowles It is hereby certified thaterror appears in the printed specification of the' above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column l line 61,` for "statisfactory" read satisfactory =5 column 7,lines 49 and 50.E :Eor "deconteaminating"' read deeontaminating --5 line59, after "its" insert kept "-5 column 9, line 7l, for "merely of readmerely for column 10V lines 2 and 3, for "eomprisnq read comprisingo;

line 53I for "fraction", first occurrence,7 read fractions (SEAL) IAttest: ERNEST W. SWIDER Attesting Ocer ARTHUR W. CROCKER 7 ActingCommissioner of Patents

7. IN THE METHOD FOR REFORMING IN CONTACT WITH A NITROGEN-SENSITIVESOLID CATALYST A STRAIGHT RUN NAPHTHA IN ADMIXTURE WITH A THERMALNAPHTHA WHICH INITIALLY CONTAINS A RELATIVELY HIGH CONCENTRATION OFORGANIC NITROGEN COMPOUNDS EQUIVALENT TO AT LEAST ABOUT 30 P.P.M.NITROGEN, THE IMPROVEMENT WHICH COMPRISES CONTACTING IN AN AUXILIARYREACTION ZONE SAID NITROGEN CONTAINING THERMAL NAPHTHA WITH HYDROGEN INTHE PRESENCE OF A NITROGENINSENSITIVE CATALYST UNDER SEVEREHYDRODENITROGENIZING CONDITIONS WHEREBY THE CONTENT OF ORGANIC NITROGENCOMPOUNDS WITHIN THE BOILING RANGE OF SAID THERMAL NAPHTHA ISSUBSTANTIALLY REDUCED, MIXING THE EFFLUENT FROM SAID AUXILIARY REACTIONZONE WITH A MAJOR PROPORTION OF SAID STRAIGHT RUN NAPHTHA, CONTACTING INA PRIMARY REACTION ZONE SAID MIXTURE WITH HYDROGEN IN THE PRESENCE OF ANITROGEN-SENSITIVE SOLID CATALYST UNDER CONDITIONS LESS SEVERE THAN INSAID AUXILIARY REACTION ZONE TO OBTAIN A PRIMARY REACTION ZONE EFFLUENTCOMPRISING C1+ HYDROCARBONS, HYDROGEN, AND HYDROGEN COMPOUNDS OFNITROGEN AND SULFUR DERIVED FROM THE ORGANIC NITROGEN AND SULFURCOMPOUNDS PRESENT IN SAID THERMAL NAPHTHA AND STRAIGHT RUN NAPHTHA,SEPARATING SAID EFFLUENT INTO PLURALITY OF FRACTION INCLUDING A C5+HYDROCARBON FRACTION OF SUBSTANTIALLY REDUCED NITROGEN CONTENT ANDREFORMING SAID C5+ HYDROCARBON FRACTION IN CONTACT WITH ANITROGENSENSITIVE SOLID CATALYST.